Several different methods have been used to attempt to change the wavelength of light. Four wave mixing (FWM) is a χ nonlinear process where two pump photons are converted to a signal and idler photon, leading to amplification of a signal light beam and wavelength conversion to an idler beam. The new wavelength (idler wavelength) of the light is restricted by the wavelengths of the pump and signal. Four wave mixing has been demonstrated in silica fibers and also in silicon waveguides.
The Raman Effect is a non-linear process where a vibration in the material (phonon) changes the wavelength of a signal photon to a new wavelength. The new wavelength is restricted by the material and the original signal wavelength. This has been demonstrated in silica fibers and also in silicon waveguides.